Radio wave guide



May 24, 1949.

w. E. BRADLEY 2,471,021

RADIO WAVE GUIDE Original Filed Aug. 15 1944 2 Sheets-Sheet 1 WILLIAM E.BRADLEY ATTORNEY INVENTOR. 53

May 24, 1949. E, BRADLEY 2,471,021

RADIO WAVE 'GUIDE 2 Sheets-Sheet 2.

Original Filed Aug. 15, 1944 FIG.5

FIGJO.

INVENTOR." WILLIAM E. BRADLEY BY ATTORNEY Patented May 24, 1949 *mesneassignments, to Philco Corporation, Philadelphia, Pa, a corporation ofPennsylvania Original application August 15, 1944, Serial No. 549,618.Divided and this application August 31, 1944, Serial No. 552,174

11 Claims. 1.,

application is 'a division -ofmy application Serial No. 549,618; filedAugust 1 5', 1944, now abandoned, and relates in general tothe fields ofultra-high frequency signal transmission and more particularlycon'cerns'hovel means for gen erating particular modes of wavetransmission.

In micro-wave transmission in wave guides and in various otherapplications; it is often desirable to transmit a single oscillationmode. For example, for transmission over a considerable distance, it iswell known that the 'I'Eor mode of propagation is that which involvesthe lowest attenuation loss.

Moreover, for certain directional antenna structures, it is desirabletodrive with a-particular oscillation mode in order to obtain therequired directional characteristic, as for example a horizontallypolarized energy distribution pattern omnidirectional in the horizontalplane. antenna array comprising a plurality of stacked biconical hornsupon a slotted cavity resonator gives an excellent horizontalpolarization act'eristic 'of high directivity. The antenna-structure issimpler and has lower loss than the conventi'onal stacked di-pole arrayand is better adaptedto operation on: ultra high frequencies. It.therefore has considerable application in micro-wave transmission.

However, in order to -obtain auniform circular energy distribution fromthe stacked biconica'l' horn antenna, it has been found that excitationmust be accomplished by the TEOl mode of oscillation. Should other modesenter the drivin cavity towards this positive antenna, the fielddistribution pattern ate. distance from the antenna will no longer bequite circular, -but will have pronounced symmetrical lobes, the numberof which will be determined by the nature of the spurious oscillationmodes. For example, it has been found that attempts to excite a'TEor-oscillation mode have been accompanied by the generationof aconsiderable TE21 mode in a circular pipe.

Since the T1321 oscillation can exist in'a smaller diameter pipe thanthe Thin, it is ordinarily difficult to remove this spurious mode. Inthe stacked biconical horn antenna structure, the TE21 wave Will resultin a pronounced four-way symmetry over the circular horizontal fielddistribution obtained by the TEM wave alone.

In the past, attempts togenerate the low'a'ttenuation TEm oscillationmode have been accomplis'hed by complex driving apparatus and haveresulted in an inpure wave, including several other oscillation-modes.

It has thus become thepractice to attempt to resonate the antennastruts-- tu-re whenever possible for the 'IEor wave order that maximumpower output at this modecould be obtained.

My. invention contemplates a wave guide transmission system including anumber of transducers permitting the excitation in one central cavity ofthe T1301 wave in its pure state.

In order to excite the 'IEo1 mode in a circular wave guide, my inventioncontemplates the use of a driving network which couples into thecircular wave guide through symmetrically-arranged slots, excited to anequal extent in the same time phase with respect to the circular wave ofthe TEM mode and in the same sense. Feeding energyinto the wave guidethrough aslot prevents any longitudinalfield and thus prevents couplingtomodes having longitudinal patterns.

such phase as to excite the 'IEoi mode.

'IEzr mode.

It is therefore an object "of my invention. to

provide means vfor generating the 'I'Eor wave in.

its pure state.

Another object of .my invention: is to: provide transducers for couplingan oscillating:sourceto a wave guide or thelike which-will transmit onlythe T-Eor oscillation mode.

A further object of my invention isv-toxprovidea a means for coupling arectangular Waveguideto a hollow circular waveguide in such 'a mannerthat the transmitted wave excited intheiguideis essentially the 'TEormode.

Another objectof my invention i z t'oigenerate the TEm oscillation modein pure form in a onciilar wave guide.

Still another object of my invention is to utilize a novel arrangementof symmetrical slits in an end plate of a Wave guide resulting in thegenera'tion of a 'IEm wave.

These and other objects of my invention will now become apparent fromthe-following sp'ecii'ication taken in connection with the accompanyingdrawings in-which:

'Figure l is a general diagrammaticrepresentation 'ofa stack biconicalhorn antenna structure coupled to a wave guide in which the "'IEbr waveis excited.

Figure 2 is a front view of one system-for excitinga 'TEti wave ina'circular wave guide.

Figure 3 is a top View of the Wave guide structure illustrated in Figure2.

Figure 4 is a perspective view of the wave guide structure illustratedin Figures 2 and 3.

Figure 5 is a perspective of a wave guide show ing the T1311 mode.

Figure 6 is an end view showing the transverse mode TEn.

Figure '7 is a perspective of a wave guide with a 'IMoi mode.

Figure 8 is a longitudinal section of Figure 7.

Figure 9 is a cross-section of a wave guide showing the TE21 mode.

Figure 10 is an elongated section of Figure 9.

Figure 11 is a cross-section of a wave guide showing a TEUI mode.

Figure 12 is an illustration of the field distribution at slits in aplate.

In Figure 1, there is illustrated an antenna structure which presentscertain decided advantages when driven by a TE-n signal. This antennastructure comprising essentially a stacked biconical horn array iscommonly utilized to develop a field distribution having a uniformcircular horizontal pattern. That is to say, the signal strengthradiated from the structure illustrated in Figure 1 when excited by theTE-n wave is independent of azimuth.

Basically, the antenna structure consists of a segmental cavityresonator 2!. This cavity resona'tor comprises essentially a length ofwave guide which is closed at the lower end by an adjustable metallicplate 53, and at the upper end by a movable piston-type plate 23. Themovable closure 23 is utilized to resonate the cavity 2i at the desiredfrequency.

Extending from the outer wall of the cavity resonator iii are aplurality of plates 24, alternate ones being inverted, and in contactwith each other as illustrated by the plates 25 and 26. cavity resonator2! is excited as illustrated by energy fed over a hollow wave guide H2.The hollow wave guide H2 is, as will be more fully explainedhereinafter, excited by the T301 mode only.

The coupling from the cavity for the biconical horns illustrated inFigure 1 is obtained by circumferentially slitting the cavity 2! as at3!. The circular slits extend about the entire perimeter of the cavitybetween the stacked metallic plates as 25 and 23. The supporting meansfor maintaining the cavity segments such as 2! in the proper spacedrelation are not illustrated but of course comprise conventional highfrequency insulating means.

By the use of the single resonant cavity illustrated, it is possible byproper placement of the circumferential slits to obtain a highly intensefield pattern in the horizontal plane.

The biconical stacked horn arrangement illustrated in Figure 1 isillustrative of an ultra-high frequency system which is best operativefrom a source of TEo1 electro-magnetic waves. Thus, with the use of TEoiwaves in the cavity illustrated, the electric field is horizontal at allpoints and circular about the axis of the cavity. Accordingly, the fieldpattern radiated through the slits 3| and between the flared hornstructure is essentially an intense horizontally polarized signal andhas omnidirectional vertical activity. The circumferential slits such as3! are placed in a location wher the waves radiating therefrom are inphase and form as intense a beam as is possible on the horizon. In theillustrated construction, the slits are shown of uniform width,

The.

although this need not always be the case. For example, in the threeelement structure shown, in order to further suppress side lobes, Iprefer to make the center gap approximately fifteen per cent wider thanthe outer gaps, the latter being kept uniform.

This antenna structure which has lower loss and has far greater utilitydue to its simplicity than the stacked dipole array is dependent forproper operation upon the excitation of the TE01 waves in pure form inthe cavity 2!. In the following description, various means will beillustrated embodying my invention for generating a TEOI wave. It is tobe understood that the application of the transducers to be described isnot necessarily limited to the biconical horn antenna disclosed inFigure l, but may be utilized wherever transmission of micro-wave for aconsiderable distance is required.

In order to more fully explain the operation of my novel transducers, abrief review of modes and structures for launching them will be given.

In Figures 5 to B, I show cavity modes in the order of their appearancesas the frequency is raised. When the pipe is large enough to containseveral modes, the modes which actually exist depend on the type oflauncher.

The first mode that will appear is the TE'n, shown in Figure 5. Asshown, the TEn is a transverse mode, the electric fields running fromthe top to the bottom of the pipe. Between points where there are largeelectric fields, there are nodal planes where the electric fieldvanishes. In the case of a traveling wave in the guide, this wholepattern is rushing along the guide and the pattern seems to move fasterthan the speed of light. In a cavity the pattern stands still, theelectric field just reversing its phase at radio frequency. That is thefirst mode that appears. This mode obviously has polarization. It willappear with a polarization determined by the launcher and must bereceived in a suitable manner. A dipole would do for the launcher andreceiver.

The next is a TMo mode shown in Figure 6. This mode shows nopolarization. The electric field is shown by the arrows. It isconveniently excited by a launcher consisting of a simple quarter-waveantenna standing in the center along the axis.

The TE'21 shown in Figure '7 is the next mode. Like the 'IEn it ispurely transverse, there being no longitudinal electric lines.

Figure 8 is the T5201. There are any number of them beyond these modes,but these will sufiice for the present discussion. In the TE01 mode, theelectrical field nowhere touches a metal surface.

The Thin is obviously suitable for the radiation of horizontalpolarization through a circumferential slot as shown in Figure l.

I have discovered that such a mode can be launched by opening a waveguide into a cavity through a symmetrical arrangement of slots. If, forexample, two opposed slots are provided in the bottom of a wave guidefed from a suitable Wave guide, it is possible to drive the two slotsexactly out of phase and the TEM mode whose electric field crosses bothslots in the same sense is coupled into the wave guide. The TEn will notbe excited since the Thin has a diametrical electric field across it. Itwill not couple to TMor because no net longitudinal electric field isset up.

With an orientation as shown by the two slots in solid lines in Figure9, the TE21, however, will also-be excited; In this figure; the isshowndotted in the form in which it will becoupled. Ins the neighborhood ofthe slots, there will be electric fields which will be parallel to theelectric field of the slots and the phase will be such as to-be excitedby two slots which are driven with thesense of field shown by the solidarrows.

Figures 2to 4 are illustrative of a simple conveniently constructedtransducer embodying the above principles in. which slots are excitedsymmetrically and. symmetrical branches of wave guides are provided forgenerating the TEoi transmission: mode in: a circular. wave guide. Thisis calledia gallery or two-way drive associated with a critical lengthtobalance out the TEZl mode.

Asillustrated, a circular hollow wave guide 4| is coupled near oneend-thereof to a transducer 42: compr-ising essentially a rectangularwave-guide extending from the source of high frequency energy; Thehollow wave guide 4| may be coupled? to whatever system is being drivenby the ultra-high frequency energy, such as the cavity of. the biconicalhorns of Figure 1.

At: junction point 43, the rectangular wave guide 42 is split. to form aT joint thereat. The two sections of wave guide. extending from thejoint 43 are circularly bent as best illustrated in Figure 3. tostraddle the circular wave guide 4-|= and form curved sections 44 and45. The cross-section. of the. curved sections 44 and 45 is of. courserectangular similar to the main guide 42;.

The two circular extensions 44 and 45 of the rectangular. wave guide.42. are plugged at 46 and 41, Figure 3, respectively, by rectangularplates. Atdiametrically opposed points and 52-, the cylindricalwaveguide 4| and the wave guide extensions 44. and 45 are slotted as isbest illustrated in Figure 2. These slots 5| and 52 are theelectro-magnetic coupling openings between the rectangular guide 42 andthe circular guide 4|.

Asis illustrated in Figure 3, the distance measured along. thecircumference between the rectangular slot 52 and the metallic plug 41is substantially equal to one-half the wave length in guide 45-. Thiscondition is also true for the distance between the slot 5| and themetal plug 46.

By. adjustment of the position of the plug with respect. to the slot,the inductance due to the peculiar place of the slit in the guide iscompensated out. When the location of these two little plugs arefound,.they are soldered in place. The cross-sectional dimensions ofthese branch guides must be carefully chosen by determining what theinput impedance of these two slots will be for theTEoi mode.

It will. now be apparent from the above that the'slots will have aninduction field having the proper polarization or'sense of phase whichwill tend todrive the TEM- In other words, the slots will be excited inpush-pull provided the lengths of. the branch guides 44 and 45 areequal.

This gallery type of drive will, however, also excitethe TE21 as alreadyexplained in connection' with Figure 9, although it will successfullyavoid excitation of TEn and TMoi. To balance outthe TEZI it isefiectively short-circuited. This is effected by sealing one end'of: thecircular Wave guide 4| by an adjustable circular metal plate 53 as shownin Figure 4. By appropriately determining; the. length between therectangular slots SI.- and: 52' and the metal plate 53, the TE21 modeof-oscillation may be. completely suppressed within the circular waveguide- 4|. That is to say, by'properly choosing the aforementionerf(1151' tance, the: energy oi-"tliissv undesiredr'm'm dscill.

lation mode which enterstiromi thez rectangular: guide 42- maybecompletelw balanced out. This:

distance is: somewhat: critical: andz-ris'a arr integral 1 number ofhalfwavelengthswi the". TE21. mode;

as measured from theefl'ectiveacenten otrl slots 5 if and-52'.

The drive mechanisnrillustrated' is :suchz as}. to permit only: thedesired 'IEdr. oscillation: mode to: exist within: the circul'anwaveaguide; 4|. As is. well known, this particularr mode will.be;-trans+- mitted' down the guide: withi mi'nimumza. attenua. tion. Forthe particular; transducer illustrated in Figures 2 to 4', the two-awaysymmetry provided by the rectangular. slots? 5| and. 52 permit thetransmission of: the: 'IEorwave: and the metal.

plate 53 results in the balancing out of. undei-- sired oscillationmodes:

The principle of operation of: the transducer.

illustrated in Figures 2 andiBumay be summarized. by the general.statement that thecircular Wave guide is energized from a transducercomprising two diametrically opposite slots having two-way symmetry inthe circumferential. or angular dimension. The TEoiand TEfn are, as.will now be clear,- produced. The'I'Ezr mode" is suppressed: by sealingone end of the guide at a critical; distance from'the slots;

To excite the TEor mode, there=mustbe produced at-each slot anequal-"component ofielectromotive force in the samephase andin acircumferential direction. 'I'hel'ength of the guide from the point ofjunctions-to the slots must be such that both slots are drivenequally.This maybe done bythe gallery arrangement here:

illustrated or in any other construction which will effect such equaldrives of the two slots.

It will now be clear that-thiswave guidein which a pure-TEor Wavehasbeengenerated, maybe coupled to the resonant cavity 2| of the stacked hornantenna array and a horizontally polarized wave is thusdeveloped.

The circular wave guide 62, as already stated, is chosen such that itsdiameter is greater than-- that required totransmit the-TE'oi mode.However, this diameter is small'erthanthat required for transmission ofthe next higher mode.

If, however; it is desired totransmit this energy in a larger diameterpipe, and accordingly minimize attenuation, a flared fitting l l (Figure1)- may be used' as a coupler between wave guide section 62 and larger"diameter circular wave guides 2 directly coupled in the illustrationhere to the cavity of the conical horn antenna.

As the TEZl mode is completely suppressed as As this oscillation mode istransmitted with minimum attenuation, it is clear'that transmission ofhigh frequency energy-over considerabledistances as, for example,inter-city communication, may bebest accomplishedby this arrangement,the wave guide of which may be of the ond circular wave guide, saidfirst wave guide having two branches extending on opposite-sides" ofsaid second wave guide, a symmetrical arrangement of slots diametricallyopposed in said second circular wave guide, a symmetrical arrangement ofslots diametrically opposed in said first wave guide and in juxtaposedrelation with said first mentioned slots in said circular wave guide forproviding a coupling between said second circular Wave guide and saidfirst wave guide, means for driving said slots from the first wave guidein the same time phase with respect to the TE01 mode and in the samephase for exciting the TEM mode in said second wave guide.

2. In a high frequency system, a first rectangular wave guide conductinghigh frequency energy, a second circular wave guide, said first waveguide having two branches extending on opposed sides of said secondcircular wave guide, a symmetrical arrangement of slots in the walls ofsaid second circular wave guide adjacent to the walls of said first waveguide, a symmetrical arrangement of slots in the walls of said firstwave guide adjacent to the walls of said second wave guide, said slotsbeing juxtaposed with respect to each other for coupling said secondwave guide to said first wave guide, means for exciting said slots insaid first wave guide equally in such phase as to excite the TEOl andIE-21 modes in said second wave guide, and means within the second waveguide for balancing out the T1321 mode.

3. In a high frequency system, a first rectangular wave guide conductinghigh frequency energy, a second circular wave guide, said first waveguide having two branches extending on opposed sides of said second waveguide, a symmetrical arrangement of slots in the walls of said firstwave guide adjacent the walls of said second wave guide, a symmetricalarrangement of slots in the walls of said second wave guide adjacent thewalls of said first wave guide, said slots in said first wave guidebeing juxtaposed to the slots in said second wave guide for couplingsaid second wave guide to said first wave guide, said slots being indiametrically opposed relation with respect to each other, and means forexciting said slots in said first wave guide equally and in such phaseas to excite the TEM mode in said second wave guide.

4. a high frequency system, a first rectangular wave guide conductinghigh frequency energy, a second circular wave gide, said first waveguide having two branches extending on opposed sides of said second waveguide, a symmetrical arrangement of slots in the walls of said firstWave guide adjacent the walls of said second wave guide, a symmetricalarrangement of slots in the walls of said second wave guide adjacent thewalls of said first wave guide, said slots being juxtaposed with respectto each other for couplin said second wave guide to said first waveguide, means for driving said slots from the first wave guide in thesame time phase with respect to the TEM mode in said second wave guide,and means within the second wave guide for balancing out the TE21 mode.

5. In a high frequency system, a rectangular wave guide conducting highfrequency energy, a second Wave guide, a third wave guide having twobranches, said rectangular Wave guide being joined to said third waveguide at the junction of the two branches, the branches extending toopposite sides of said second wave guide and slots formed in said twowave guide branches, and said second wave guide in diametrically opposedrelation with respect to each other, said slots of said two wave guidebranches being juxtaposed to the corresponding slots of the second waveguide, said slots being symmetrically arranged to receive equal and inphase energy from said rectangular wave guide.

6. In a hi h frequency system, a rectangular wave guide conducting highfrequency energy, a second wave guide, a third Wave guide having twobranches, said rectangular wave guide being joined to said third waveguide at the junction of the branches, the branches extending toopposite sides of said second wave guide and slots formed in said twowave guide branches, and said second wave guide, said slots of said twowave guide branches being juxtaposed to the corresponding slots of thesecond Wave guide, said slots being symmetrically arranged to receiveequal ener y from said rectangular wave guide, and a closure for saidsecond wave guide at a critical distance from said slots for balancingout the TElzi mode.

7. In a high frequency system, a rectangular wave guide conducting highfrequency energy, a second wave guide, a third wave guide having twobranches, said rectangular wave guide being joined to the third waveguide at the junction of the two branches, the branches extending toopposite sides of said second wave guide and slots formed in said twoWave guide branches and said second wave guide, said slots of said twowave guide branch-es being juxtaposed to the corresponding slots of thesecond wave guide, said slots being symmetrically arranged to receiveequal energy from said rectangular wave guide, said wave guide branchesbeing closed at their ends at a distance to the slots formed thereinsubstantially equal to one half wave length.

8. In a high frequency system, a rectangular Wave guide conducting highfrequency energy, a second Wave guide, a third wave guide having twobranches, said rectangular wave guide being joined to the third waveguide at the junction of the branches, the branches extending toopposite sides of said second wave guide and slots formed in said twoWave guide branches and said second wave guide, said slots of said twowave guide branches being juxtaposed to the corresponding slots of thesecond wave guide, said slots being symmetrically arranged to receiveequal energy from said rectangular wave guide, the cross-sectionaldimensions of said wave guide branches being determined by the inputimpedance of the slots for the 'IEor mode.

9. In a high frequency system, a rectangular wave guide conducting highfrequency energy, a second Wave guide, a third wave guide having twobranches, said rectangular wave guide being joined to the third waveguide at the junction of the branches, the branches extending toopposite sides of said second wave guide and slots formed in said twowave guide branches and said second wave guide, said slots of said twowave guide branches being juxtaposed to the corresponding slots of thesecond wave guide, said slots being symmetrically arranged to receiveequal energy from said rectangular Wave guide, and a closure for saidsecond Wave guide placed from the effective center of said slots, adistance determined by an integral number of half wave lengths of theTE21 mode.

10. In a high frequency system, a rectangular wave guide conducting highfrequency energy; a circular wave guide having diametrically opposedslots, and a transducer extending from said rectangular to said circularwave guide for coupling said wave guides, said transducer comprisll'lgtwo diametrically opposite slots juxtaposed to said slots in saidcircular wave guide having two way axial symmetry in the circulardimension.

11. In a high frequency system, a rectangular wave guide conducting highfrequency energy; a circular wave guide having diametrically opposedslots, and a transducer extending from said rectangular to said circularwave guide for coupling said wave guides, said transducer comprising twodiametrically opposite slots juxtaposed to said slots in said circularWave guide having two Way axial symmetry in the circular dimension, saidcircular wave guide being closed at one end at a critical distance fromsaid slots for suppressing the TE21 mode.

WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 19382,206,923 Southworth July 9, 1940 2,241,119 Dallenbach May 6, 1941 102,401,751 Friis June 11, 1946 FOREIGN PATENTS Number Country Date417,564 Great Britain Sept. 29, 1934

